Nanosecond and steady-state fluorescence techniques will be used to investigate the structure and function of enzymes and of model membranes. New fluorescence probes based on known excited-state reactions will be developed. These reactions include excimer and exciplex formation and excited-state proton transfer. Use will be made of the information that has emerged regarding these processes from studies in photophysics. The new fluorescence probes to be developed should be of value for automated clinical assays. Nanosecond time-resolved emission spectroscopy will be used to investigate solvent relaxation at biological sites of interest including enzyme active sites and regions of bilayer lipid membranes. Nanosecond time-dependent emission anisotropy techniques will be used to measure segmental flexibility in proteins and to obtain information about the complex rotational motions of probes in bilayer lipid membrane vesicles.